Multi-plate centrifugal clutches are known as, for example, launch clutches for motorcycles and the like. See, for example, Japanese Patent Publication 2003-322177 and Japanese Patent Publication 2004-125059. Japanese Patent Publication 2003-322177 describes a multi-plate centrifugal clutch including a plate group in which a plurality of drive plates and a plurality of driven plates are alternately arranged, a clutch input shaft that rotates together with the drive plates, and a pressure plate having roller weights.
When a motorcycle or the like starts moving, the rotational speed of the clutch input shaft increases and the roller weights receive a centrifugal force. A part of the centrifugal force is converted into a pressing force in a thrust direction, and the plate group is pressed by the pressure plate which receives the pressing force. As a result, the state of the clutch changes from a disengaged state to an engaged state. Conversely, when the motorcycle or the like stops, the rotational speed of the clutch input shaft decreases and the centrifugal force applied to the roller weights is reduced accordingly. As a result, the pressing force applied to the pressure plate is also reduced and the state in which the drive plates and the driven plates are in frictional contact with each other is canceled. Thus, the state of the clutch changes from an engaged state to a disengaged state.
In the above-described multi-plate centrifugal clutch, the clutch input shaft has an oil supply passage that extends in an axial direction and an oil supply channel that extends outward in a radial direction. When the clutch input shaft rotates, oil supplied via the oil passage is ejected from the oil supply channel and sprayed around by the centrifugal force, thereby lubricating the roller weights, the pressure plate, the drive plates, and the driven plates.
In the above-described prior art multi-plate centrifugal clutch, a portion of the oil sprayed from the oil supply aperture in the clutch input shaft is supplied to the roller weights, and the amount of oil supplied to the roller weights is relatively small. In addition, the oil supply line for supplying the oil to the roller weights is the same as the oil supply line for supplying the oil to the plate group. In other words, the oil supplied to the roller weights and the oil supplied to the plate group are ejected from the same oil supply aperture. Therefore, most of the oil ejected from the oil supply aperture is supplied to the plate group, and only a small amount of oil is supplied to the roller weights.
It has been considered unnecessary to supply a large amount of oil to the roller weights because the frictional force generated at the roller weights is not very large. However, the inventors of the present invention have found that abnormal noise is occasionally generated when the roller weights come into contact with an outer peripheral portion of the pressure plate and that the abnormal noise can be reduced by supplying a sufficient amount of oil to the roller weights. Also, the life of the roller weights can be increased and the reliability of the multi-plate centrifugal clutch can be improved by supplying a sufficient amount of oil to the roller weights.